http://bodyrecomposition.com/Miscarticles/youarenotdiffere.html
It doesn't matter what their initial weight is either ~
That's a difference more profound than skintone, skeletal proportions, and so forth.
Some people have more than one sinus node (the nerve nexus that tells the heart to beat). It's an hereditary condition, as is the ability to survive lengthy immersion in cold water, or to eat seal livers on a regular basis.
Not everybody is the same!
The current world record for surviving immersion and suffocation in extremely cold water is 6.5 hours. It's held by a woman from the Northernmost part of Norway. The holder of the earlier record was also held by an individual from the same area, as was the even earlier record, and all the way back to roughly 14,000 BC (or thereabouts).